1. Field of the Invention
The present invention relates to a nonvolatile semiconductor device, and in particular, to a nonvolatile semiconductor memory device having a memory cell array with a multilayer structure.
2. Description of the Related Art
Flash memories in which memory cells having a floating gate structure are NAND- or NOR-connected to form a memory cell array have been well known as conventional nonvolatile memories that is electrically rewritable. In addition, ferroelectric memories are also known as nonvolatile memories that make high speed random access possible.
Meanwhile, resistance change memories using variable resistance elements as memory cells have been proposed as a technology for further miniaturizing memory cells. As for the variable resistance elements, phase change memory elements whose resistance value changes as a chalcogenide compound switches between a crystal and an amorphous state, MRAM elements in which the resistance changes due to the tunneling magnetoresistive effects, memory elements of a polymer ferroelectric RAM (PFRAM) in which resistive elements are formed of a conductive polymer, ReRAM elements in which resistance changes through the application of an electrical pulse, and the like are known (Patent Document 1: Japanese Patent Application Laid-Open No. 2006-344349, paragraph 0021).
In these resistance change memories, memory cells can be formed of a series circuit of a Schottky diode and a variable resistance element instead of a transistor, and therefore, a cross point structure in which memory cells are placed at intersections of upper and lower wires can be used. Thus, there are advantages in that it is easy to form and can be further integrated (Patent Document 2: Japanese Patent Application Laid-Open No. 2005-522045). In addition, a memory cell array can have a multilayer structure in these resistance change memories so that the capacity of the nonvolatile memory can be increased.
In the case where memory cells are laminated in different orders in the memory cell array during the process for forming a nonvolatile memory having such a multilayer structure, however, the properties of the memory cells become inconsistent in the memory cell array, which causes an error in the program operation, reading operation and the like.